Heart failure is a debilitating disease in which abnormal function of the heart leads in the direction of inadequate blood flow to fulfill the needs of the tissues and organs of the body. Typically, the heart loses propulsive power because the cardiac muscle loses capacity to stretch and contract. Often, the ventricles do not adequately eject or fill with blood between heartbeats and the valves regulating blood flow become leaky, allowing regurgitation or back-flow of blood. The impairment of arterial circulation deprives vital organs of oxygen and nutrients. Fatigue, weakness and the inability to carry out daily tasks may result. Not all heart failure patients suffer debilitating symptoms immediately. Some may live actively for years. Yet, with few exceptions, the disease is relentlessly progressive.
One particular form of heart failure is diastolic heart failure (DHF) wherein systolic function is generally preserved but diastolic function is compromised, i.e. there is a significant degree of diastolic dysfunction. Diastolic dysfunction refers to an abnormality in the ability of the heart to fill during diastole, which is the phase of the cardiac cycle when the ventricles relax and fill with blood prior to contraction.
Current methods (such as echocardiography) to measure diastolic function within patients so as to detect diastolic dysfunction and DHF are not being routinely used clinically, especially on asymptomatic patients. Accordingly, diastolic dysfunction can remain undetected for years within a patient until symptoms develop.
Hence, there is a need to provide improved techniques for monitoring or evaluating diastolic function within a patient. Many patients with heart failure that have, or are susceptible to, diastolic dysfunction already have pacemakers, ICDs or CRT-Ds implanted therein (or are candidates for such devices.) (A CRT-D is a cardiac resynchronization therapy device with defibrillation capability.) Accordingly, it is desirable to provide such devices with the capability to monitor diastolic function and to detect and track diastolic dysfunction within the patient, such that suitable warning signals can be generated or other appropriate actions can be taken. The invention is generally directed to these ends.